A flute
33 ± 3 flutes per foot, the deepest standard flute. Used where cushioning and stack strength matter more than print detail.
Pick by flute and strength
A corrugated box is chosen twice: first by the flute that suits the product and the print, then by the strength figures written into the specification. This page compares the five standard US flutes in millimetres and flutes per foot, and sets out the ordered procedure from product weight to a finished box spec.
01
Thickness in millimetres and flutes per foot tell you how the board will print and how much cushioning it gives. A 4.8 mm A flute and a 0.8 mm F flute are different tools, not different grades of the same tool.
02
The bursting or edge crush value, the size limit as L + W + D, and the gross weight limit are the three lines that make a specification comparable between suppliers.
03
Board moisture between 6.5 and 9.5 percent keeps the edge crush reading honest. Outside that range the same board tests differently, which is why the check closes the procedure.
Match the flute to the product weight and the print detail first, then confirm the number in the table.
A flute is 4.8 mm thick at 33 ± 3 flutes per foot, the deepest of the five standard US flutes. C flute is 4.0 mm at 39 ± 3 and B flute 3.2 mm at 47 ± 3. The deeper flutes give more cushioning and more board between the liners, which is why A, B and C dominate shipping work.
E flute measures 1.6 mm at 90 ± 4 flutes per foot and F flute 0.8 mm at 125 ± 4. At those flute counts the outer liner sits close to a flat surface, so fine retail print holds detail that a deep A flute cannot reproduce.
The tolerance matters when two boards are compared: 33 ± 3 flutes per foot means the count can sit between 30 and 36 without leaving specification. Read the tolerance together with the thickness, not separately.
33 ± 3 flutes per foot, the deepest standard flute. Used where cushioning and stack strength matter more than print detail.
47 ± 3 flutes per foot. Thinner than C with good flat crush, common where a shorter flute still has to survive handling.
39 ± 3 flutes per foot. The standard shipping flute: enough depth for protection, enough flute count for a workable print surface.
90 ± 4 flutes per foot. The outer liner sits close to flat, so retail print holds fine detail.
125 ± 4 flutes per foot, the finest print surface of the five. Thickness is half of E flute, so it behaves closer to solid board.
Board outside this range tests differently and scores crack. The check closes the box-choice procedure at the packing line.
A box specification lists the bursting or edge crush test, the size limit (length plus width plus depth) and the gross weight limit.
| Flute | Thickness | Flutes per foot | Flutes per metre |
|---|---|---|---|
| A | 4.8 mm | 33 ± 3 | 108 ± 10 |
| B | 3.2 mm | 47 ± 3 | 154 ± 10 |
| C | 4.0 mm | 39 ± 3 | 128 ± 10 |
| E | 1.6 mm | 90 ± 4 | 295 ± 13 |
| F | 0.8 mm | 125 ± 4 | 420 ± 13 |
| Board moisture | 6.5–9.5% | — | — |
| Medium basis weight (US) | 130 g/m² | 0.026 lb/ft² | — |
| Corrugator speed | 150 m/min | ≈500 ft/min | — |
Flute dimensions, test definitions, basis weights, moisture range, corrugator speed and patent dates as published in corrugated industry references.